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951.
Nicoleta Gabriela Hădărugă Daniel Ioan Hădărugă Heinz-Dieter Isengard 《Journal of inclusion phenomena and macrocyclic chemistry》2013,75(3-4):297-302
Cyclodextrins are some of the most used carriers for bioactive compounds (as host–guest complex) and many factors influence the association–dissociation of this complex, some of them being related to hydrophobicity. In the solid state, cyclodextrins contain two types of water molecules: “surface” water molecules (especially close to the crystal surface) and “strong-bonded” water molecules (especially from the cyclodextrin cavity), but the classification is hard to do, and the concentration of these water molecules are relatively difficult to estimate by simple methods. In the present study we used the volumetric Karl Fischer titration to estimate these types of water molecules in cyclodextrins by means of the rate of water reaction (related to diffusion from cyclodextrin crystals). “Surface” water molecules are titrated with rates between 1.8–2.8 mM/s for α-cyclodextrin, while for β-cyclodextrin these rates are little bit higher (2.9–3.4 mM/s). The rates corresponding to “strong-bonded” water molecules are approximately tens fold lower (0.05–0.3 mM/s for α-cyclodextrin and 0.15–0.33 mM/s for β-cyclodextrin). The approximate ratio between “surface” and “strong-bonded” water molecules could also be estimated by this simple and rapid method. 相似文献
952.
Pascal Munier Marie-Béatrice Giudicelli Dominique Picq et Daniel Anker 《Journal of carbohydrate chemistry》2013,32(8):1225-1230
Abstract L'hydrolyse acide des acétals et en particulier des osides fait intervenir un carbocation intermédiaire stabilisé par l'oxygène voisin; un substituant électroattracteur en α de l'atome d'oxygène ou de carbone d'un tel cation déstabilise cedernier et rend l'hydrolyse des acétals plus difficile. C'est ainsi que pour un 2-méthoxy-tétrahydropyrane, le remplacement en C-6 d'un groupement CH2OH par CO2Et1 provoque une diminution de la vitesse d'hydrolyse d'un facteur de 200. Il est également bien connu que les 2-désoxy glycosides sont hydrolysés bien plus rapidement que leurs analogues 2-hydroxylés. Le même résultat est obtenu avec un atome d'halogène; c'est ainsi que Horton et coll.2 en introduisant un atome d'iode en position 2′ d'analogues de la daunorubicine et de l'adriamycine ont pu augmenter leur efficacité in vivo. Compte tenu de la taille réduite de l'atome de fluor qui modifie peu l'encombrement de la molécule, plusieurs travaux ont été consacrés à l'introduction d'un fluor en position 2 d'osides pour ralentir leur vitesse d'hydrolyse in vivo. 3-5 Cette même démarche a conduit d'autres auteurs à synthétiser des 2,2-difluorosucres.6 On pouvait donc envisager de remplacer l'hydrogène en C-1 de certains sucres par un groupement trifluorométhyle pour obtenir ainsi une nouvelle classe d'osides, dont la liaison osidique serait très stabilisée, ce qui devrait accroître leur durée de vie in vivo; on sait en effet 7 que les acétals de trifluorométhylcétones sont très difficiles à hydrolyser. Nous avons récemment décrit8 l'obtention des composés 1 et 9 et, on pouvait envisager de substituer l'hydroxyle anomérique de tels 2-uloses par divers nucléophiles. Les substitution nucléophiles en α d'un groupe CF3 sont difficiles9,10 et font en général intervenir un carbocation du type CF3-C+R1-XR2 stabilisé par un hétéroatome X(O, S)11-15 ou par un phényle.9 Ce carbocation est formé dans quelques cas par voie électrochimique,14-15 mais, dans la plupart des travaux, il résulte soit de la rupture d'une liaison CR1-Y assistée par un acide de Lewis soit de la solvolyse de cette liaison.9 Pour éviter l'emploi d'un acide de Lewis incompatible avec des groupes protecteurs acido-sensibles, nous avons mésylé l'hydroxyle anomérique pour obtenir un meilleur groupe partant. Nous décrivons dans cette note les résultats préliminaires obtenus principalement par action de divers nucléophiles sur ces mésylates. 相似文献
953.
Diamino‐ and diazidofuranoses represent useful precursors, for example, for the synthesis of substituted nucleosides and metal complexes, respectively. Known procedures for their synthesis lack the availability of cheap starting materials, adequate yields, and the access to all possible diastereomeres. Therefore, 3,5‐diazido‐3,5‐dideoxy‐ and ‐2,3,5‐trideoxyfuranoses both with ribo‐ and xylo‐configuration were prepared using different approaches. 相似文献
954.
Aïcha Mbarek Geneviève Chadeyron Daniel Avignant Damien Boyer Mohieddine Fourati Daniel Zambon 《Journal of Sol-Gel Science and Technology》2013,68(2):193-203
The sol–gel chemistry route has successfully been used to prepare samples of LnP5O14 (Ln = La, Gd) pentaphosphates from lanthanides chlorides and phosphorous pentoxide dissolved in isopropanol. Crystallized powders of single phase were obtained after calcination of gels at 350 °C. The structural characterizations of materials were investigated by means of X-ray diffraction as well as infrared and Raman spectroscopies, whereas their thermal behavior has been studied by differential thermal analyse and thermogravimetric analyses. Powders morphology was analyzed by means of scanning electron microscopy and laser granulometry. The photoluminescence properties of the Eu3+ ions in sol–gel derived LaP5O14 and GdP5O14 samples were investigated and compared with homologous samples synthesized by the conventional solid state reaction. 相似文献
955.
956.
Prof. Dr. Sjoerd Harder Dominik Naglav Dr. Christian Ruspic Prof. Dr. Claudia Wickleder Dr. Matthias Adlung Dr. Wilfried Hermes Dr. Matthias Eul Prof. Dr. Rainer Pöttgen Dr. Daniel B. Rego Prof. Dr. Frederic Poineau Prof. Dr. Kenneth R. Czerwinski Prof. Dr. Rolfe H. Herber Prof. Dr. Israel Nowik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12173-12173
957.
Dr. Christoph Hirschhäuser Dr. Juraj Velcicky Dr. Daniel Schlawe Dr. Erik Hessler Dr. André Majdalani Dr. Jörg‐Martin Neudörfl Dr. Dr. Aram Prokop Dr. Thomas Wieder Prof. Dr. Hans‐Günther Schmalz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13017-13029
The synthesis and stereochemical assignment of two classes of iron‐containing nucleoside analogues, both of which contain a butadiene? Fe(CO)3 substructure, is described. The first type of compounds are Fe(CO)3‐complexed 3′‐alkenyl‐2′,3′‐dideoxy‐2′,3′‐dehydro nucleosides (2,5‐dihydrofuran derivatives), from which the second class of compounds is derived by formal replacement of the ring oxygen atom by a CH2 group (carbocyclic nucleoside analogues). These compounds were prepared in a stereoselective manner through the metal‐assisted introduction of the nucleobase. Whilst the furanoid intermediates were prepared from carbohydrates (such as methyl‐glucopyranoside), the carbocyclic compounds were obtained by using an intramolecular Pauson–Khand reaction. Stereochemical assignments based on NMR and CD spectroscopy were confirmed by X‐ray structural analysis. Biological investigations revealed that several of the complexes exhibited pronounced apoptosis‐inducing properties (through an unusual caspase 3‐independent but ROS‐dependent pathway). Furthermore, some structure–activity relationships were identified, also as a precondition for the design and synthesis of fluorescent and biotin‐labeled conjugates. 相似文献
958.
Dr. Damien Hudry Dr. Christos Apostolidis Dr. Olaf Walter Dr. Thomas Gouder Dr. Eglantine Courtois Dr. Christian Kübel Dr. Daniel Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(17):5297-5305
Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well‐defined actinide‐based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non‐aqueous surfactant‐assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra‐small diameters of 1 nm) of thorium oxide were synthesised. 相似文献
959.
Dr. Kuppuswamy Arumugam C. Daniel Varnado Jr. Dr. Stephen Sproules Dr. Vincent M. Lynch Prof. Dr. Christopher W. Bielawski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(33):10866-10875
High yielding syntheses of 1‐(ferrocenylmethyl)‐3‐mesitylimidazolium iodide ( 1 ) and 1‐(ferrocenylmethyl)‐3‐mesitylimidazol‐2‐ylidene ( 2 ) were developed. Complexation of 2 to [{Ir(cod)Cl}2] (cod=cis,cis‐1,5‐cyclooctadiene) or [Ru(PCy3)Cl2(?CH‐o‐O‐iPrC6H4)] (Cy=cyclohexyl) afforded 3 ([Ir( 2 )(cod)Cl]) and 5 ([Ru( 2 )Cl2(?CH‐o‐O‐iPrC6H4)]), respectively. Complex 4 ([Ir( 2 )(CO)2Cl]) was obtained by bubbling carbon monoxide through a solution of 3 in CH2Cl2. Spectroelectrochemical IR analysis of 4 revealed that the oxidation of the ferrocene moiety in 2 significantly reduced the electron‐donating ability of the N‐heterocyclic carbene ligand (ΔTEP=9 cm?1; TEP=Tolman electronic parameter). The oxidation of 5 with [Fe(η5‐C5H4COMe)Cp][BF4] as well as the subsequent reduction of the corresponding product [ 5 ][BF4] with decamethylferrocene (Fc*) each proceeded in greater than 95 % yield. Mössbauer, UV/Vis and EPR spectroscopy analysis confirmed that [ 5 ][BF4] contained a ferrocenium species, indicating that the iron center was selectively oxidized over the ruthenium center. Complexes 5 and [ 5 ][BF4] were found to catalyze the ring‐closing metathesis (RCM) of diethyl diallylmalonate with observed pseudo‐first‐order rate constants (kobs) of 3.1×10?4 and 1.2×10?5 s?1, respectively. By adding suitable oxidants or reductants over the course of a RCM reaction, complex 5 was switched between different states of catalytic activity. A second‐generation N‐heterocyclic carbene that featured a 1′,2′,3′,4′,5′‐ pentamethylferrocenyl moiety ( 10 ) was also prepared and metal complexes containing this ligand were found to undergo iron‐centered oxidations at lower potentials than analogous complexes supported by 2 (0.30–0.36 V vs. 0.56–0.62 V, respectively). Redox switching experiments using [Ru( 10 )Cl2(?CH‐o‐O‐iPrC6H4)] revealed that greater than 94 % of the initial catalytic activity was restored after an oxidation–reduction cycle. 相似文献
960.
Dr. Nina Schützenmeister Dr. Michael Müller Prof. Dr. Uwe M. Reinscheid Prof. Dr. Christian Griesinger Dr. Andrei Leonov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(51):17584-17588
Here we report the synthesis of all four stereoisomers of mefloquine. Mefloquine (Lariam) is an important anti‐malaria drug that is applied as a racemate of the erythro form. However, the (?)‐isomer induces psychosis, while the (+)‐enantiomer does not have this undesired side effect. There are six syntheses of which five lead to the wrong enantiomer without the authors of these syntheses noting that they had synthesized the wrong compound. At the same time physical chemistry investigations had assigned the absolute configuration correctly and the last enantioselective synthesis that took these results into account delivered the correct absolute configuration. Since various synthetic approaches failed to provide the correct stereoisomers in previous syntheses, we submit here a synthetic approach with a domino Sonogashira‐6π‐electrocyclisation as key step that confirmed synthetically the correct absolute configuration of all four isomers. 相似文献